Each year between 6000 and 7000 infants in the U.S. die with a diagnosis of sudden infant death syndrome (SIDS). The most compelling hypothesis regarding the pathophysiology of SIDS suggests that infants who die suddenly have abnormalities in cardiorespiratory control. Efforts to prevent SIDS deaths are hampered by an inability to identify infants at risk prior to the event and the inadequate understanding of the physiologic processes leading to the terminal event. Documented monitoring with event recording of transthoracic impedance (TTI)/ECG signals preceding, during, and following respiratory and cardiac alterations has recently become available and provides the investigator with a useful tool to study infants at risk for life-threatening events. The specific aims of this study are to use state of the art event recording technology to evaluate infants at increased risk for fife threatening events in order to 1) improve quality of home monitoring, 2) determine compliance in monitor use, 3) obtain physiologic parameters of cardiorespiratory episodes. A multicenter network will be established to study approximately 2000 patients at increased risk for life-threatening events: preterm infants with symptomatic apnea at discharge, infants who have experienced an apparent life-threatening event (ALTE) without an identifiable cause, and subsequent siblings of SIDS victims. Baseline studies will include hematocrit, reticulocyte count, echocardiogram, cranial ultrasound, hair analysis for illicit drugs, growth parameters, and neurodevelopmental assessment. Event recording with TTI/ECG and pulse oximetry will be initiated on admission to the study and continued for 6 months. Subsequent laboratory evaluation at 6 and 12 months of age will include hematocrit, reticulocyte count, echocardiogram and neurodevelopmental assessment. Patients will be contacted weekly and examined monthly in the outpatient clinic. Event recording will be analyzed to determine 1) the frequency, duration, and type of respiratory, cardiac and desaturation alterations, 2) physiologic significance of these alterations, 3) their relationship to clinical outcome (abnormal echo, developmental delay, poor growth, and/or death), and 4) compliance with monitor use. The results of this study will demonstrate the natural history of cardiorespiratory alterations in at risk infants, provide insight into the cardiorespiratory mechanisms operative in life-threatening events in infants at risk for SIDS, and improve the overall use of home monitors in managing at risk infants.